1. Field of the Invention
This invention relates to a method for setting an end portion of a bundle of thread-like bodies, and more particularly to a method for setting an end portion of a bundle of solid thread-like bodies or hollow thread-like bodies made of any polymeric material which is suitable for selective or differential permeation fluid separations, such as blood dialysis, with a solidifiable liquid in a casing assembly.
2. Description of the Prior Art
A hollow-fibre permeability apparatus has been used for blood dialysis, by which toxic materials can be removed from the blood of a patient suffering from renal failure or intoxication. Such an apparatus is also used as an artificial lung, in which oxygen and carbon dioxide are exchanged through hollow-fiber membranes to serve as an artificial lung.
An example of a conventional hollow-fibre permeability apparatus will now be described.
FIG. 1 shows a hollow-fibre blood dialysis apparatus 10 currently used as an artificial kidney. The apparatus 10 comprises a cylindrical casing assembly 1 made of synthetic resin. The casing assembly 1 is open at both ends. Upper and lower cylindrical enlarged-diameter portions 37 and 38 are formed integrally with the casing assembly 1. An inlet tube 2 and an outlet tube 3 for introducing a dialysate are connected to the enlarged portions 38 and 37, respectively, which are positioned diametrically opposite to each other. Screw threads 8 are formed on the outer cylindrical surfaces of the end portion of the enlarged portion 37 and of the end portion of the enlarged portion 38.
A permeating region 25 in the casing assembly 1 is occupied with a hollow-fibre bundle 6 which consists of numerous hollow fibres 5 packed tightly to each other. The hollow fibres 5 are made of any polymeric material, such as cellulose, and are substantially of the same length as the casing assembly 1. Usually, the bundle 6 consists of ten to fifteen thousand hollow fibres 5, which are about 0.3 mm in diameter. The total effective membrane area of the hollow fibres 5 for dialysis is about 1 m.sup.2.
Each end portions of the cylindrical casing assembly 1 is closed by a fluid-tight case wall member (potting material) 7 preferably formed of polymeric composition such as polyurethane, silicone resin or epoxy resin. The hollow fibers 5, substantially parallel to each other and to the axis of the cylindrical casing assembly 1, extend between the potting materials 7. The hollow fibers 5 have open end portions which are embedded in and extend through the cast wall member (potting material) in fluid-tight relation thereto. Upper and lower disc covers 13 contact the outer peripheral regions of the upper and lower surfaces of the potting material 7. Fastening rings 17 and 18 are secured to the casing assembly 1 by the engagement of screw threads 21 with the screw threads 8. Thus, the potting material 7 and the disc covers 13 are tightly fixed between both ends of the casing assembly 1 and inwardly directed flange portions 19 of the fastening rings 17 and 18. In this way, the bundle 6 of hollow fibres 5 is fixed at both ends in the casing assembly 1. The openings of the hollow fibres 5 on the smooth surfaces of the potting material 7 are made by cutting the cast wall member along the predetermined lines.
The disc covers 13 at the both ends of the casing assembly have blood inlet 14 and outlet tube 15, respectively. The disc covers 13 forms circular compartments 20 adjacent to and communicating with the inlet or outlet tubes 14 or 15, and also communicating with the interiors of the hollow fibres 5.
In the case of blood dialysis, dialysate 35 is supplied into the housing 1 from the inlet tube 2, and blood 36, from an artery of a patient, is introduced into the housing 1 through the inlet tube 14. The dialysate 35 is distributed in an annular space 22 defined by the enlarged portion 38, and then passes into the bundle 6 of hollow fibres 5. The dialysate 35 passes upwardly along through the bundle 6, and comes out of the housing 1 through the outlet tube 3 via an annular space 23 defined by the enlarged portion 37 and out of the housing 1 through outlet tube 3. The blood 36 is distributed into the upper openings of the hollow fibres 5 in the upper compartment 20. The blood 36 flows downward counter-currently with the dialysate through the interiors of the hollow fibres 5, and is led out of the housing 1 through the lower openings of the hollow fibres 5, the lower compartment 20 and the outlet tube 15.
The blood of a renal failure patient, containing metabolic wastes such as urea, uric acid and creatinine can be removed from the blood 36 into the dialysate 35 through permeable membranes of the hollow fibres. The purified blood 36 returns to a vein of the patient. When the dialysate side is negative in pressure compared with the blood side, ultra-filtration is effected through the hollow fiber membrane, thus excess water can be removed from the blood 36 of the patient. The apparatus 10 can be smaller than conventional coil-type or plate-type (Kiil-type) apparatus, because the hollow fibres 5 provide a relatively large effective membrane area for its size. Thus, the blood priming volume can be reduced, being beneficial to patients during their dialysis therapy. The hollow fiber type is also easier to handle, and is superior for ultrafiltration.
In the assemblage of the blood dialysis apparatus 10, the end portions of the bundle 6 consisting of numerous hollow fibers 5 should be potted in the cylindrical case assembly 1. Conventional operations for potting the bundle 6 in the case assembly 1 are very troublesome.
In one example of the conventional operations, the hollow fiber bundle 6 is first placed in the case assembly 1 which is about 30 cm long. The bundle 6 is protruded by about 3 to 5 cm from both the ends of the case assembly 1. Next, one of the protrusions of the bundle 6 is dipped into a solidifiable liquid in a molding cavity. The solidifiable liquid is, for example, silicone resin composition, epoxy resin composition or urethane resin composition. When the protrusion of the bundle 6 is dipped into the solidifiable liquid, the wicking usually occurs between and along the hollow fibers, due to capillar action. The wicking takes place usually about 3 to 5 cm above the predetermined level of the solidifiable liquid. The solidifiable liquid rises much higher at the central portion than in the peripheral portion of the bundle.
Many studies have been made to prevent the wicking of the solidifiable liquid in the container. However, there has been no useful way except a centrifugal method which is effective in achieving a uniform fluid-tight wall and seal between those hollow fibers and the casing assembly, without wicking.
The following is a discussion on the capillary action in view of preventing the wicking phenomenon.
It is considered that the capillary action is closely correlated with "wetting". We have a relationship with respect to a wetting work Wi, a surface tension .gamma.s of solid material (ie. the capillary tube), and an interfacial tension .gamma.i between the liquid and the solid material, as follows: EQU Wi = .gamma.s - .gamma.i (1)
Further, the relationship between a surface tension .GAMMA.l of the liquid, the surface tension .gamma.s of the solid material and the interfacial tension .gamma.i is represented by the following formula: EQU .gamma.s = .gamma.i+.gamma..sub.l .multidot.cos.theta. (2)
where .theta. represents contact angle between the solid material (ie. the capillary tube) and the liquid. The formula (2) is called "Young's relationship". From the above formulas (1) and (2); we have EQU Wi = .gamma.l.multidot.cos.theta. (3)
From the formula (3), it is inferred that the wetting work Wi which relates to the wicking depends on the contact angle O, in other words, depends on the wettability.